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BIG PHYSICS, BIG QUESTIONS –

Science : Tadpoles rule the nursery by behaving badly

By Alison Motluk

WHEN two species of tadpole share a pond, one thrives at the expense of
the other. They do it not by attack but by bullying, an American researcher told
the annual meeting of the Animal Behavior Society in College Park, Maryland,
this week.

Past explanations of which species comes out on top have ranged from mouth
size to the release of growth-inhibiting agents into the water. But Sarah
Faragher, a PhD student at Northern Arizona University in Flagstaff, says that
the way tadpoles act can be just as important.

Faragher studied two species, the southern leopard tadpole, Rana
utricularia, and the green tree tadpole, Hyla cinerea, which have
coevolved in southwestern Louisiana. “There hasn’t been a lot of work on tadpole
behaviour,” admits Faragher.

She found that in her laboratory the leopard, which grows up to 83
millimetres long, swam aggressively towards the green tree tadpole, only half
its size. Southern leopards “harassed” green trees 2.5 times as often as they
did members of their own species. Green trees seemed to expend energy just
staying out of the way, she says.

Faragher then measured the growth of the harassed tadpoles. She found that
being bullied inhibits their feeding. “They grow significantly less when in
trials with southern leopards than when alone.” Faragher is now doing
experiments in the wild to see if, given the choice, green trees will pick sites
that contain no leopard tadpoles.